Sunday, December 2, 2018

Lake Crescent and Landlsides

A trip around the Olympic Peninsula typically entails a drive along the shore of Lake Crescent on the northwest of the Peninsula. The lake is one Washington State's largest. By area it is number 6, but by volume it is number 2 behind Lake Chelan.

Lake Crescent 

The lake is within a glacially eroded valley on the northwest flank of the Olympic Mountains. The valley was not carved by ice coming out of the Olympics, but by the massive Juan de Fuca ice lobe that covered much of the area well up the flank of the Olympics.

The depth of the lake has taken awhile to get a handle on because it is so deep. Dartnell, Warrick, and Wegmann (2017) completed a bathnmetry study and came up with a result similar to a depth of a previous effort by Eian Ray and Jeff Enge. These more recent efforts have found a maximum depth of about 600 feet.

The more recent bathymetry shows what appears to be a landslide on the lake floor. The over steep mountain slopes in this glaciated area have failed in the past with several large scale landslides recognized in the area of the lake.

Portion of Schasse (2003) compilation geology map
Blue hatcher line shows estimated elevation of glacial ice
Note several large landslides in yellow

The landslide at the east end of the lake has been interpreted to have dammed the lake, splitting the lake into two lakes, Lake Sutherland and Lake Crescent. This deepened Lake Crescent by about 50 feet and the lake began draining to the northwest via the Lyre River. This new drainage arrangement allowed a new species of fish to develop associated with the lake. 

If one looks carefully while driving Highway 101, the ground between the two lakes is hummocky typical of large landslide deposits. Other slide deposits are evident as well. 

Slide deposit above east shore of lake

The highway crosses a large slide complex to the west of the lake as well.

Lidar bare earth image of slide complex west of Lake Crescent via DNR Lidar Portal

The lake is located in the transition zone between the very wet west side of the Olympic Peninsula a dn the drier north and northeast rain shadow side of the Olympic Mountains.

Lake Crescent and with Storm King Mountain in the distance

Cloud bank on the west ridge of Pyramid Mountain

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